1. Field of the Invention
The present invention relates to low friction swivel joints having zero backlash in tension and compression.
2. Prior Art
Several different types of hydrostatic and hydrodynamic bearings have been used in swivel joints. U.S. Pat. No. 3,392,995 shows a pressure balanced bearing which is used for reacting loads, but which utilizes a mechanical valve to provide pressure for functioning. Further, continuous hydraulic fluid flow is required in the joint. As disclosed, hydraulic oil must either flow into or out of the joint. Further, if the sealing surface of the reaction pad does not remain perpendicular to the load axis as the joint swivels side loads will be encountered, resulting in friction and requiring higher torques to overcome such frictional loads. The amount of swivel is quite limited in the device shown in this patent.
U.S. Pat. No. 4,099,801 discloses a spherical seat hydrostatic bearing that depends on a continuous flow of high pressure fluid to function.
U.S. Pat. No. 3,314,336 illustrates a "compression only" swivel which, again, has a sealing surface that does not rotate with the axis of the cylinder, which causes side loading of the ball used relative to the socket. High torque is required to overcome this friction when the joint swivels. Further, the bearing device does not have any type of a "floating" piston, which means that the pressure in the bearing tends to become increasingly out of phase with the pressure in the cylinder that is being used with the bearing as frequency increases. Considerable leakage also will be experienced in this device as the ball shifts across the socket due to phase differences in that there is no positive seal of the swivel chamber. The pressure in the swivel is exactly the same as the pressure in the cylinder being used, which limits the size of the parts that can be designed. Limited swiveling also appears to be a problem with this type of device.
U.S. Pat. No. 3,169,807 shows a spherical air or fluid bearing without any seals or pressure compensation. Two other patents of general interest to hydrostatic bearings on cylindrical objects with O rings extending around the cylinder to form generally sealed annular chambers included U.S. Pat. Nos. 3,360,309 and 3,863,995.
Pressure balanced hydrostatic bearings which permit sliding movement between planar surfaces, and which accommodate a limited amount of swiveling are shown in U.S. Pat. No. 3,921,286. The device shown includes a sealed area on the outer planar surface of a piston that is used to contain fluid under a pressure which is a function of the pressure under the piston. U.S. Pat. No. 3,994,540 shows a pressure compensated bearing wherein a sealed area forming a hydrostatic pad is maintained at a pressure equal to the pressure under the piston of the bearing. The pressure in the bearing is controlled by means sensitive to shifts in position between the supported object and a supporting surface at a location which is spaced from the actual support bearing itself.
In both of these devices, planar support surfaces for permitting sliding movement between two objects are disclosed. No spherical seat which has a sealed pressure area reacting against a socket or mating spherical surface is shown.